1. Field of the Invention
The present invention relates generally to a rear projection apparatus in which an image is projected from the rear onto a screen, and is directed more particularly to a rear projection apparatus in which a convex lens, such as a Fresnel lens, is arranged so that its optical axis is eccentrically positioned in relation to the center of the screen.
2. Description of the Prior Art
In prior art rear projection apparatus of this kind, in order to utilize effectively the image light projected from a light source (light emitted from the phosphor of a cathode ray tube or the like), a lenticular screen is used to give different directivities to the projected light between the vertical and horizontal directions and a Fresnel lens to improve the luminance distribution are employed together. Further, the optical axis of the Fresnel lens is shifted from the picture center of a screen to change the direction of luminous flux to the viewer, or to converge the projected light to the viewer so that there is provided an optimum viewing area at which the viewer can enjoy a bright picture.
To this end, in the prior art rear projection apparatus of this kind, there is provided a mechanism to slidably move the Fresnel lens up and down and accordingly move its optical axis up, down and to thereby change the direction of the luminous flux emitted from the screen.
According to the prior art rear projection apparatus, however, it is required that the Fresnel lens must be made larger than the size of the screen by an amount at least equal to the amount that it is moved up and down. If the lens and screen were the same size and the optical axis of the lens were moved off the central axis of the screen, a portion of the screen would not have the benefit of the improved luminance distribution of the lens. This requires that there must be provided in the framework for attaching the screen a holding member that can slidably guide and support the larger Fresnel lens therein. Therefore, the cabinet of the rear projection apparatus naturally becomes unacceptably large in size.